Northern Harrier question

I was at my local adubon and last week around 3 in the afternoon I spotted a young bird, but only had my 70-200F4 and 20D.
I have a 100-400, but was wondering If these birds frequent an area or wander quite a bit.
In other words might I see this bird again, and is a 100-400 enough?

Harriers often hunt on the same grounds frequently.

Whether a 100-400 is enough depends on how close you are able to get to the Harrier.

The Harriers I've observed hunted about 3 farm fields and would make the rounds to each one. I guess it depends on the size of the area they're hunting if they'll come back...most likely they will.

Harriers do frequent the same territory while hunting. Ones that I have observed definitely stick to a particular flight pattern and can offer some great photo opportunities since they'll often fly nearly the exact same route every time.

Thats great info, and what I was hoping for. I was going to post an image, but it was so far away.